In case of the coexistence of implants and natural teeth in the oral cavity, we need to consider the strength of occlusal contact, because there is a difference of tissue displacements between implants and natural teeth. However, regarding the optimum occlusal contacts of superstructure of implant prosthesis, there are still many unclear points. Therefore, we simulated the effect of occlusal contact states on load distribution for implants and natural teeth to establish a guideline for the occlusal contact of a superstructure of implant prosthesis.
For natural teeth which have good periodontium (the first premolar) and an osseointegrated implant, we made a graph expressing the relation of the occlusal pressure and the amount of tissue displacement. Based on the graph, we simulated the amount of tissue displacement and the load distribution at the centric occlusal position between natural teeth, between a natural tooth and an implant, and between implants.
The results were as follows: Load distribution on the implant part without a periodontal ligament was large. However, in the early stages of chewing,the load of an implant and a natural tooth became comparable by giving a gap. In addition, during strong biting, the load of an implant and a natural tooth was comparable giving no gap, but if giving a gap larger than 20 μm， there was a case when the load distribution on a natural tooth was larger than that on an implant.
In conclusion, it is suggested that it is not necessary for the superstructure of implant prosthesis to have lighter occlusal contact than natural teeth.
Hydroxyapatite (HA) coated implants were evaluated by surface structure analyses using a surface roughness meter, an energy dispersive X-ray fluorescence spectrometer (EDX), an X-ray diffractometer and a scanning electron microscope (SEM). The seven implants used in this study were the POI implant system of Japan, AQB implant system of Japan, SPLINE implant system of USA, MAESTRO implant system of USA. PLATON implant system of Japan, TAPERED screw MP-1 of USA, and APT implant being developed in Japan. The HA coating techniques of AQB, MAESTRO, TAPERED, and SPLINE are plasma spraying, PLATON is thermal decomposition, and APT is sputtering. The roughness average (Ra) of the surface of HA coated films was in the range of 1.8-5.9 μm and the orders were AQB＞SPL＞MAE=TAP=POI＞APT＞PLA. The adhesion strength of film to substrate was largest in APT and the order of the strength was APT＞MAE＞AQB=PLA=SPL＞TAP＞POI. The thickness of the HA films was less than approximately 5 μm in PLATON and homogeneous 1-2 μm in APT. On the other hand, the thickness by the plasma spraying and the flame spraying techniques was in the range of 20 to 90 μm. The porosities of the HA films were calculated from the weight and volume of the HA films. The HA films of the APT implant were dense, while the HA films coated by plasma spraying and flame spraying techniques were porous. Significant changes in solubility and pH were not observed in each HA-coated implant.
JIS types 2 and 4 titanium and Ti-6Al-4V alloy have been used for dental implantation. Because of the carcinogenicity of vanadium, the use of Ti-6Al-7Nb alloy containing niobium with easy passive state has been evaluated. To develop more suitable implant materials, we performed basic experiments to compare the mechanical properties of JIS types 2 and 4 titanium, Ti-6Al-4V alloy,and Ti-6Al-7Nb alloy. As a result, proof strength and hardness were highest in Ti-6Al-4V, and lowest in JIS type 2 titanium. Surface analysis showed that the oxygen concentration was higher in JIS type 4 than in type 2 titanium. Fine precipitates of vanadium and niobium were observed in Ti-6Al-4V and Ti-6Al-7Nb alloys, respectively. Other components were evenly distributed. As for Ti-6Al-7Nb alloy, the results of hardness and proof strength showed that it could be used as an implant material. It is thought that in vivo tests are necessary in the future.
The aim of this study was to investigate the viscoelastic properties of the implant-tissue interface for different loading positions.
The viscoelastic properties of six implants were measured using an automatic mobility diagnostic system that we developed. The three parameters, viscosity c1, viscosity c2 and elasticity k were automatically obtained using a personal computer. Measurement points were taken at four different positions, the implant abutment, and the superior, middle and inferior portions of the impression post. Variations among measurement points were studied for each of the obtained dynamic parameters by 2-way ANOVA at a significance level of 0.05.
All of the parameters were the largest at the implant abutment position and the values decreased from the lower to the upper positions of the impression post. This indicates that large values for the parameters viscosity c1, viscosity c2 and elasticity k imply less movement (less mobility). A significant difference among the four positions was recognized in all parameters by 2-way ANOVA.
We concluded that it is necessary to standardize the measurement positions and to pay attention to the height of the prosthesis in comparison with implant length in the case of long-term clinical evaluations by examining and diagnosing the status of contact between the placed implant and its surrounding bone.
A resonance frequency analyzer (Osstell mentor: OSM, Integration Diagnostics) has been developed as a device for evaluating the intraosseous stability of implants.Implant stability quotient (ISQ) values derived from the device are intended to be employed as indices for evaluating intraosseous stability. The aim of this study was to find any changes over time in ISQ values in two-stage dental implants.
Test sites selected included upper jaw anterior implants (UA group), upper posterior implants (UP group), and lower posterior implants (LP group). For ISQ values, we made one measurement from each of the buccal, lingual or palatal, mesial and distal sides.Measurements of ISQ values were made at stage-one surgery (O1), stage-two surgery (O2), superstructure cementation (SC), and one year later (1Y). Items for analysis were 1)reliability of ISQ values, 2)changes of ISQ values over time for each implant site, and 3) relevance of ISQ values at O1 and 1Y.
1. It was revealed that ISQ values increased in reliability as a result of employing the average value of measurements made from 4 directions. 2. In all the groups, changes over time for ISQ values showed similar tendencies. The values increased from O1 to SC, but there was no difference between SC and 1Y. In addition, the LP group marked higher values than the UA and UP groups at all the measurement times. 3. The relation between O1 and the difference between 1Y and O1 was found to be a negative correlation in all groups.
ISQ values measured were found to have high levels of reliability. Changes in ISQ values from O1 to 1Y were revealed. It was also found that the lower the ISQ values at O1, the greater the increase of ISQ values during the test. On the contrary, the higher the ISQ values at O1, the lower the increase of ISQ values during the test.
Removal of residual strain in titanium materials caused by machining leads to decreases in their tensile strength and hardness. However, such a decrease is not considered to be problematic provided their strength is sufficient to bear occlusal pressure. Furthermore, the elongation percentage of titanium materials of certain diameters deviates from the standard value established by JIS, leading to decreases in their fatigue destruction strength. It is considered that if the fatigue destruction strength can be improved, stable mastication can be obtained for a long time after implantation. Therefore, heat treatment of titanium materials with different diameters was performed at 350, 400, and 450°C, and its influence on their mechanical properties was evaluated in this study.
The tensile strength and hardness of titanium materials before treatment were higher in the order of 4mm＞5 mm＞3 mm in diameter. The tensile strength and hardness decreased by heat treatment. On the other hand, the elongation percentage of titanium materials before treatment was higher in the order of 3 mm＞5 mm＞4 mm in diameter. The elongation percentage of the 4-mm material deviated from the standard value established by JIS. The elongation percentage of each diameter titanium material increased by heat treatment. The increase was highest in the 4-mm titanium material heated at 450°C, and its elongation percentage was within the standard value established by JIS. Furthermore, the increase in the elongation percentage was lowest in the 3-mm titanium material. After heating titanium materials, oxygen, nitrogen, and carbon were slightly diffused on the surface layer. Metallographic observation revealed that the morphology of crystal grains differed among titanium bars with different diameters.
Purpose: Loss of teeth,loss of occlusal loading, and general skeletal status are associated with a reduced trabecular bone pattern of the mandible. Little is known about whether implant placement also has an effect. We compared the long-term changes in fractal dimension (FD) of the trabecular bone pattern in mandibular molar regions that had implant placement with others that did not.
Methods: Thirty-one subjects (12 men and 19 women) aged 54 to 91 years (mean±SD, 65.5±8.0 years) were recruited for this study.All had undergone at least two panoramic radiographs at intervals of 3 years or more. Radiographs were digitized at 300 dpi. At both baseline and follow-up, FD was calculated on digitized radiographs of 51 edentulous molar sites of the mandible, of which implants were subsequently placed in 28 sites. A linear multiple regression analysis, adjusted for possible covariates, was performed to estimate the effect of implant placement on the change in FD between baseline and follow-up radiographs. Furthermore, in 10 subjects aged 54 to 76 years (mean±SD,64.5±6.6 years) who had one implant placement site and one edentulous site, each in a different molar region of the mandible, FD of these two sites were compared through dependent sample t-tests.
Results: A multiple regression analysis of the 51 molar sites revealed a potential association between implant placement and increased FD, although it did not reach statistical significance (p=0.253). There were marginally significant differences in the changes in FD in implant placement and edentulous sites on differing sides of the mandible in 10 subjects (0.023±0.020 vs. -0.005±0.047, p=0.063).
Conclusions: Our results imply an increased complexity in the trabecular bone pattern of the mandible. Implant placement may contribute to improvement of the trabecular bone pattern of the mandible. A further investigation including a large number of subjects would be necessary to confirm our findings regarding the beneficial effect of implant placement on the internal structure of the mandible.
A day surgery unit (DSU) was established at Kyoto University Hospital in January 2000. Dental implants and related surgery are performed in the DSU by our department. The purpose of this research was to investigate problems with implants and related surgery at the DSU.
In this study, the subjects were 61 patients (male 32,female 29) under general anesthesia with standardized protocols from May 2000 to May 2004. For outpatient surgery, major problems were bleeding from the nose and throat with intra-nasal intubations, postoperative nausea and vomiting (PONV), and pain after operation. We coped with nasal bleeding using a relatively small intubation tube. For PONV, opioid and nitric oxide gas were avoided during anesthesia. Nonsteroidal anti-inflammatory drugs (NSAID) were used before operation as a pre-emptive analgesia. During operation, local anesthesia was used positively. After operation, NSAID and local anesthesias were administered. After operation, patients were moved to the recovery room for observation of general and local physical conditions. Their physical status was evaluated by the Aldrete Score, and when they fulfilled specific standards, they were moved to the step down recovery room. In this room, they were evaluated for general status and permission for going home by the Postoperative Discharge Scoring System. The next day, a medical examination by interview was performed. The operations included implant placement in 32 cases, abutment connection in 5 cases, bone graft for alveolar bone augmentation in 14 cases, sinus lift in 9 cases, and alveolar distraction in 1 case. Average surgery time was 114 ± 39 min (40-213min), average anesthesia time was 169 ± 41 min (91-265 min), and average staying time was 216 ± 46 min (135-335 min). The interview revealed pain of the wound(high 2, moderate 12, small 14, none 33), sore throat (high 4, moderate 4, small 18 and none 35), and nausea and vomiting (high 0, moderate 2, light 1, none 58).
In conclusion, it was possible to conduct safely the implant surgery accompanied by advanced surgical invasion with standardized ambulatory general anesthesia. For outpatient surgery, it is important to recover the general status smoothly; therefore it is essential to draw up a standardized patient care guideline at the time of surgery.
Reports addressing the advantages of immediate and early implant placement in extraction sockets have been increasing in number. The majority of them, however, are centered on surgical procedures, and there have been few reports focusing on longitudinal implant stability. In this study, changes in bone levels on both mesial and distal aspects of each implant in an extraction socket were monitored radiographically for assessment of implant stability. During the period from May 2002 to October 2003, a total of 36 implants were placed in 30 healthy, non-smoking patients (7 males and 23 females). Average patient age at surgery was 51.0 years (range: 20 to 78 years). Of 36 implants, 27 were immediate and 9 were early implants. These implants were followed up for at least 3 years, including clinical and radiographic assessments at the time of implant placement, final restoration and each maintenance recall. Both immediate and early implants showed favorable clinical and radiographic findings at all recalls. In the 3-year follow-up period after final restoration, marginal bone resorption was found around every implant. However, in no case did the resorption reach the border between the smooth and SLA (Sand-blasted, Large-grit and Acid-etched) rough surfaces of the fixture. The bone resorption over time was evaluated by means of Tassay, and the results were compared in terms of immediate/early placement and insertion depth. The insertion depth was classified into 3 levels in reference to the adjacent alveolar crest (Level 1:the part of the implant fixture between the smooth/rough border and implant shoulder is placed at the alveolar crest; Level 2: the implant shoulder is level with the alveolar crest; and Level 3: the implant shoulder is placed below the alveolar crest). No significant difference in bone resorption was found between immediate and early implants. As for the bone resorption relative to insertion depth, significant differences were found between Level 1 and Level 2 (p＜0.01 at Year 1, 2 and 3)and between Level 1 and Level 3 (p＜0.01 at Year 1 and p＜0.05 at Year 2 and 3). In this study, implants placed at the insertion depth of Level 1 showed least bone resorption at all assessment periods, and the resorption after 3 years was within the biological dimensions like the natural dentition, thus a favorable long-term prognosis for this approach was indicated.
Intravenous sedation under the supervision of dental anesthesiologists is an increasingly common procedure in private dental clinics performed to ensure the safety and comfort of patients undergoing oral implant surgery. A questionnaire survey of patients following dental implant surgery was conducted to assess the level of recognition/understanding of intravenous sedation,presence or absence of various types of uncomfortable events during the perioperative period, and requests/expectations of patients regarding this type of sedation.
A questionnaire was administered to a total of 55 patients who underwent intravenous sedation in a private dental clinic during the period between November 2004 and February 2006.
Only 32.7% of patients were familiar with the term “intravenous sedation”. Since a total of 90.9% of patients had no or very little memory of events during surgery, the amnestic effects of sedative agents used were considered sufficient. Only a small number of patients reported uncomfortable perioperative events such as maintenance of a posture for a long period of time and coughing due to irrigation. Almost all patients indicated that they were comfortable during the operation, though 7.3% were bothered by the absence of memory during surgery.
In order to ensure that patients can fully benefit from the amnestic effects of intravenous sedation, cooperation among the dentist, patient, and dental anesthesiologist during surgery, as well as preoperative management, is necessary.
A navigation system has recently been applied to dental implant placement. CT data obtained from helical CT have been employed for the navigation system in many cases; however, there have been no reports on the compatibility with some kinds of conebeam CT. Therefore, in this study, implant placement was performed by applying cone-beam CT slice data (3DX Multi-Image Micro CT; Morita Corporation) to the IGI navigation system (IGI; DenX Advanced Dental Systems Ltd.).The patient was a 32-year-old male with lower second premolar absence. Bone morphology in the lower second premolar region was narrow. CT was taken by 3DX, and slice data obtained were converted to DICOM. These data were reversed upside down on a computer, and subsequently transferred to the navigation system. Using the navigation system, 3-dimensional implant placement planning was performed with considering the bone morphology and position of the superstructure. The implant position at the preoperative planning was almost in accordance with the realized position, and an all-ceramic crown was inserted as the super-structure.
Implantation using a navigation system was considered useful, particularly in areas with anatomically complex bone morphology. Furthermore, it was found that data processing was necessary to apply 3DX slice data to the IGI navigation system.